[c++] Use std::future::get() instead of ::wait()

[eddelbuettel]

Closes #2319

Issue and/or context:

See #2319 for discussion

Changes:

The use of std::future::wait() is replaced by std::future::get().

Notes for Reviewer:

SC 43721

[shortcut-integration]

This pull request has been linked to Shortcut Story #43721: [c++] Asynchronous functions should use get() not wait() so that errors from Core propagate.

[codecov]

Codecov Report

Merging #2320 (f0c2ee9) into main (3346005) will decrease coverage by 0.02%.
Report is 2 commits behind head on main.
The diff coverage is 50.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2320      +/-   ##
==========================================
- Coverage   78.78%   78.76%   -0.02%     
==========================================
  Files         140      140              
  Lines       10750    10750              
  Branches      215      215              
==========================================
- Hits         8469     8467       -2     
- Misses       2183     2184       +1     
- Partials       98       99       +1     

Flag	Coverage Δ
libtiledbsoma	67.64% <50.00%> (-0.08%)	⬇️
python	90.58% <ø> (ø)
r	74.69% <ø> (ø)

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Components	Coverage Δ
python_api	90.58% <ø> (ø)
libtiledbsoma	48.69% <50.00%> (-0.16%)	⬇️